CN115259161B - Collar-shaped silicon carbide nanofiber aerogel material and preparation method thereof - Google Patents

Abstract

The invention relates to a collar-shaped silicon carbide nanofiber aerogel material and a preparation method thereof, wherein the method comprises the following steps: performing chemical vapor deposition reaction by using silicon powder, silicon dioxide aerogel powder doped with metal oxide nano particles and carbon powder to obtain collar-shaped silicon carbide nano fibers; uniformly dispersing the collar-shaped silicon carbide nanofiber with water, and then performing liquid nitrogen freezing to obtain nanofiber gel; and sequentially carrying out freeze drying and annealing treatment on the nanofiber gel to obtain the collar-shaped silicon carbide nanofiber aerogel material. The collar-shaped silicon carbide nanofiber aerogel prepared by the invention is an aerogel constructed by nano fibers with complex surface structures, wherein the nano fibers with complex surface structures are series of nano collar sleeved on the nano fiber trunk in the one-dimensional length direction at different distances on the surface, and compared with the silicon carbide nanofiber aerogel with smooth surface, the collar-shaped silicon carbide nanofiber aerogel has the characteristics of being more excellent in the aspects of mechanics, heat insulation, electromagnetic wave absorption and the like.

Description

A kind of ring-shaped silicon carbide nanofiber airgel material and its preparation method

technical field

The invention belongs to the technical field of silicon carbide nanofiber airgel, and in particular relates to a ring-shaped silicon carbide nanofiber airgel material and a preparation method thereof.

Background technique

Silicon carbide nanofiber airgel is a kind of nanoporous material formed by one-dimensional silicon carbide nanowires as building blocks by overlapping each other in three-dimensional space. It has many excellent properties such as high temperature resistance, low thermal expansion, thermal shock resistance, oxidation resistance and corrosion resistance endowed by characteristic properties. On the other hand, it has the unique flexibility, elasticity, high bending strength and Young's modulus of one-dimensional nanowires. Excellent mechanical behavior. Therefore, the prepared silicon carbide nanofiber airgel has broad application prospects in elastic heat insulation, high temperature heat insulation, electromagnetic wave absorption, filtration and adsorption in extreme thermal environment and highly corrosive environment.

It is reported in Chinese patent application CN113968582A etc. that the carbon source providing carbon monoxide gas and the silicon source providing silicon monoxide gas are subjected to chemical vapor deposition reaction under an inert atmosphere to generate silicon carbide nanofibers, and then interweave into three-dimensional silicon carbide nanofibers for gas condensation In these prepared aerogels, the surface of the silicon carbide nanofibers of the constituent units is often smooth, the connection between the silicon carbide nanofibers is poor, and the stress transmission and stress dissipation between the nanofibers are affected. The current airgel materials composed of silicon carbide nanofibers need to be further improved in terms of force, heat or electromagnetic properties.

Therefore, it is urgent to prepare a new silicon carbide nanofiber airgel material to improve the performance of silicon carbide nanofiber airgel in terms of force, heat or electromagnetic, and further meet the needs of practical applications.

Contents of the invention

In order to solve one or more technical problems in the prior art, the present invention provides a ring-shaped silicon carbide nanofiber airgel material and a preparation method thereof. The ring-shaped silicon carbide nanofiber airgel material prepared by the invention improves the comprehensive properties of the silicon carbide nanofiber airgel such as force, heat, and electromagnetic properties, and further satisfies practical application requirements.

In a first aspect, the present invention provides a method for preparing an annular silicon carbide nanofiber airgel material, said method comprising the steps of:

(1) Using silicon powder, silica airgel powder doped with metal oxide nanoparticles and carbon powder to carry out chemical vapor deposition reaction to obtain ring-shaped silicon carbide nanofibers;

(2) uniformly dispersing the ring-shaped silicon carbide nanofibers with water to obtain a nanofiber dispersion, and then subjecting the nanofiber dispersion to liquid nitrogen freezing to obtain a nanofiber gel;

(3) The nanofiber gel is subjected to freeze-drying and annealing in sequence to obtain a ring-shaped silicon carbide nanofiber airgel material.

Preferably, step (1) includes the following sub-steps:

(a) silicon powder and silica airgel powder doped with metal oxide nanoparticles are separated and placed in an independent chamber at the bottom of the graphite crucible, and covered with a graphite lid;

(b) place the graphite crucible in the corundum crucible, and completely bury the graphite crucible with carbon powder, and cover the corundum lid;

(c) The corundum crucible is completely covered with graphite paper and placed in a high-temperature atmosphere furnace for chemical vapor deposition reaction. After cooling to room temperature, collect ring-shaped silicon carbide nanofiber coarse material from the graphite cover;

(d) calcining the ring-shaped silicon carbide nanofiber coarse material to obtain the ring-shaped silicon carbide nanofiber; preferably, the temperature of the calcination is 600-800° C. 40min.

Preferably, the silica airgel powder doped with metal oxide nanoparticles is formed by mixing metal oxide nanoparticles and silica airgel powder.

Preferably, the average particle size of the silicon powder is 0.1-50 μm, preferably 2 μm; the metal oxide nanoparticles are iron oxide nanoparticles, ferric oxide nanoparticles, ferrous oxide nanoparticles, zirconia nanoparticles, One or more of titanium oxide nanoparticles, copper oxide nanoparticles, zinc oxide nanoparticles, titanium oxide nanoparticles, tin oxide nanoparticles, lead oxide nanoparticles; the average particle diameter of the metal oxide nanoparticles is 10 ~300nm is preferably 60nm; the average particle diameter of the silica airgel powder is 1-200 μm, preferably 5 μm; the average particle diameter of the skeleton particles of the silica airgel powder is 6-60 nm, preferably 20 nm and/or the mass ratio of the metal oxide nanoparticles to the silica airgel powder is (0.001-0.05):1, preferably 0.012:1.

Preferably, the mass ratio of the silicon powder to the silica airgel powder doped with metal oxide nanoparticles is 1: (0.3-1.5), preferably 1:0.8; the chemical vapor deposition reaction is at Carried out in an inert atmosphere, preferably, the inert atmosphere is argon, and when the chemical vapor deposition reaction is carried out, the pressure of the argon gas is 0.01-0.07MPa, preferably 0.03MPa; the temperature of the chemical vapor deposition reaction is 1200 ～1600°C is preferably 1350°C; the time of the chemical vapor deposition reaction is 1～8h, preferably 4h; and/or the rate of heating up to the temperature of the chemical vapor deposition reaction is 2～8°C/min, preferably 4°C/min .

Preferably, the graphite crucible is cylindrical, and the ratio of the height to the diameter of the graphite crucible is 1: (2-7), preferably 1:3.

Preferably, the ring-shaped silicon carbide nanofiber contained in the ring-shaped silicon carbide nanofiber airgel material comprises a nanofiber backbone and a plurality of nano-rings sleeved on the nanofiber backbone; preferably , the average diameter of the nanofiber trunk is 30-240nm, and the average diameter of the periphery of the nano-ring is 35-280nm; preferably, a plurality of nano-rings are sleeved on the nanofiber at unequal intervals on the trunk.

Preferably, the mass fraction of ring-shaped silicon carbide nanofibers contained in the nanofiber dispersion is 0.07%-7%, preferably 2.5%; and/or the time for liquid nitrogen freezing is 5-60 minutes, preferably 20 minutes.

Preferably, the freeze-drying is carried out in a freeze-drying machine. During the freeze-drying process, the temperature of the chamber of the freeze-drying machine is controlled to be 10-35° C., and the temperature of the cold trap of the freeze-drying machine is -80° C. to -50°C, the pressure of the freeze-drying is 1-30Pa, the time of the freeze-drying is 24-96h; and/or the temperature of the annealing treatment is 800-1100°C, preferably 900°C, the temperature of the annealing treatment The time is 0.5-12h, preferably 2h.

In a second aspect, the present invention provides the ring-shaped silicon carbide nanofiber airgel material prepared by the preparation method described in the first aspect of the present invention; preferably, the ring-shaped silicon carbide nanofiber airgel The material has one or more of the following properties: the tensile elongation at break of the ring-shaped silicon carbide nanofiber airgel material is 30-40%, and the maximum rebound rate is 100% under the maximum compression deformation of 95%; The room temperature thermal conductivity of the ring-shaped silicon carbide nanofiber airgel material is 0.018～0.021W/(m·K); the frequency of the ring-shaped silicon carbide nanofiber airgel material is 2-18GHz It has excellent microwave absorption performance in the range, the matching thickness is 3mm, the minimum reflection loss is -50~-55dB at 10.5GHz, and the effective absorption bandwidth with reflection loss <-10dB is 6.8~7.5GHz.

The present invention provides a ring-shaped silicon carbide nanofiber in a third aspect, and the ring-shaped silicon carbide nanofiber is prepared by the following method:

Using silicon powder, silica airgel powder doped with metal oxide nanoparticles and carbon powder for chemical vapor deposition reaction to obtain ring-shaped silicon carbide nanofibers;

Preferably, the silica airgel powder doped with metal oxide nanoparticles is formed by mixing metal oxide nanoparticles and silica airgel powder, more preferably, the metal oxide The mass ratio of nanoparticles to the silica airgel powder is (0.001-0.05): 1, and/or the silica powder and the silica airgel powder doped with metal oxide nanoparticles The mass ratio is 1: (0.3～1.5);

Preferably, when the chemical vapor deposition reaction is carried out, the silicon powder and the silica airgel powder doped with metal oxide nanoparticles are separated and placed in an independent chamber at the bottom of the graphite crucible, more preferably Yes, the graphite crucible is cylindrical, and the ratio of the height to the diameter of the graphite crucible is 1: (2-7).

The loop-shaped silicon carbide nanofiber airgel material prepared by the present invention has at least the following beneficial effects compared with the prior art due to the unique loop-shaped structure of the nanofiber surface that is not smooth:

(1) The ring-shaped silicon carbide nanofiber airgel material prepared by the present invention is not smooth due to the surface of the nanofiber, the surface structure is relatively complex, and the specific surface area is significantly improved, and the concave-convex non-planar structure existing in the nanofiber will make the surface of the nanofiber Mechanical interlocking between nanofibers, when subjected to uneven force, stretching, rapid thermal shock and sudden force shock, etc., the mechanical interlocking between nanofibers and the ability of nanofibers to exceed the limit force Through the occurrence of friction, the internal stress concentration is relieved, thereby preventing the expansion and expansion of micro-cracks, and finally can effectively inhibit the overall rupture of the airgel block, thereby improving the flexibility, mechanical fatigue resistance, and thermal/mechanical shock resistance of silicon carbide nanofiber airgel. and other mechanical-related properties; therefore, the ring-shaped silicon carbide nanofiber airgel material prepared by the present invention has significant advantages in mechanics compared with the smooth-surfaced silicon carbide nanofiber airgel prepared in the prior art.

(2) Due to the complex surface structure of the ring-shaped silicon carbide nanofiber airgel material prepared by the present invention, the nano-rings on the nanofiber backbone can additionally increase a large number of interfaces. On the one hand, the phonon-interface scattering is increased to make the nanofibers The thermal conductivity of the solid is low, and on the other hand, it has high infrared reflection and absorption ability, which can effectively reduce the radiation heat conduction, and the overall result is that the heat insulation ability is greatly improved; the ring-shaped silicon carbide nanofiber airgel prepared by the present invention The room temperature thermal conductivity of the material is 0.018-0.021W/(m K), the lowest is only 0.018W/(m K), while the current room temperature thermal conductivity of silicon carbide nanofiber airgel with smooth surface is generally 0.025 ~0.045W/(m K); Therefore, compared with the silicon carbide nanofiber aerogel with smooth surface prepared in the prior art, the ring-shaped silicon carbide nanofiber airgel material prepared by the present invention has better performance in thermal insulation. Significant advantage.

(3) Due to the complex surface structure, the ring-shaped silicon carbide nanofiber airgel material prepared by the present invention can greatly improve the electromagnetic wave absorption performance by effectively increasing the scattering and reflection of electromagnetic waves in a wide range of electromagnetic waves; the present invention The minimum reflection loss (RL) of the prepared ring-shaped silicon carbide nanofiber airgel material can reach -50~-55dB, and the widest effective microwave absorption band (RL<-10dB) can reach 6.8~7.5GHz, and the current surface is smooth The minimum reflection loss (RL) of the silicon carbide nanofiber airgel is generally at most -35～-45dB, and the widest effective microwave absorption band (RL<-10dB) is generally 3～5.6GHz; therefore, the collar prepared by the present invention Compared with the silicon carbide nanofiber aerogel with smooth surface prepared in the prior art, the shape silicon carbide nanofiber airgel material has significant advantages in electromagnetic wave absorption.

Description of drawings

Fig. 1 is the schematic diagram when the graphite crucible that adopts when carrying out chemical vapor deposition reaction of the present invention is placed in corundum crucible; Among Fig. 1, 1 is graphite crucible; 11: independent chamber; 2: corundum crucible; Fig. 1 is only for illustration purpose The proportions and dimensions of the various parts in the figure may not necessarily be consistent with the actual product.

Fig. 2 is a schematic diagram of a loop-shaped silicon carbide nanofiber obtained by chemical vapor deposition in Example 1 of the present invention.

Fig. 3 is a scanning electron micrograph of the ring-shaped silicon carbide nanofiber obtained in Example 1 of the present invention.

Fig. 4 is a high-resolution transmission electron microscope image of the ring-shaped silicon carbide nanofiber obtained in Example 1 of the present invention.

Fig. 5 is an X-ray diffraction diagram of the ring-shaped silicon carbide nanofiber obtained in Example 1 of the present invention.

Fig. 6 is a scanning electron micrograph of the ring-shaped silicon carbide nanofiber airgel material prepared in Example 1 of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In a first aspect, the present invention provides a method for preparing an annular silicon carbide nanofiber airgel material, said method comprising the steps of:

(1) Utilize silicon powder, silicon dioxide airgel powder doped with metal oxide nanoparticles and carbon powder (such as coke powder) to carry out chemical vapor deposition reaction to obtain ring-shaped silicon carbide nanofibers; in the present invention , the silica airgel powder doped with metal oxide nanoparticles is preferably mixed with metal oxide nanoparticles and silica airgel powder; The sources of oxide nanoparticles and silica airgel powder have no special requirements, and the products that can be purchased directly on the market or synthesized by existing methods can be used; when carrying out the chemical vapor deposition reaction, the silicon dioxide powder and the silica airgel powder doped with metal oxide nanoparticles are separated and placed in an independent chamber at the bottom of the graphite crucible; the present invention has no special limitation on the amount of the carbon powder, so that the The powder can completely bury the graphite crucible containing silicon powder and silica airgel powder doped with metal oxide nanoparticles;

(2) The ring-shaped silicon carbide nanofibers are uniformly dispersed with water to obtain a nanofiber dispersion, and then the nanofiber dispersion is frozen with liquid nitrogen to obtain a nanofiber gel (also referred to as a nanofiber cryogel) ); in the present invention, the liquid nitrogen freezing is freezing under liquid nitrogen; in the step (2) of the present invention, for example, stirring at a rotating speed of 1500 to 2500 rpm for 1 to 3 hours to obtain uniformly dispersed nanofiber dispersion liquid;

(3) The nanofiber gel is subjected to freeze-drying and annealing treatment sequentially to obtain a ring-shaped silicon carbide nanofiber airgel material; in the present invention, the ring-shaped silicon carbide nanofiber airgel material is made of The ring-shaped silicon carbide nanofiber is constructed, and the ring-shaped silicon carbide nanofiber includes a nanofiber backbone (silicon carbide nanofiber backbone) and a plurality of nano-rings (silicon carbide nanofiber backbone) sleeved on the nanofiber backbone. nano ring).

The invention provides a method for preparing a ring-shaped silicon carbide nanofiber airgel material. The ring-shaped silicon carbide nanofiber airgel material is a type of airgel formed by silicon carbide nanofibers with a complex surface structure , the complex surface structure nanofiber is that the nanofiber is covered with a series of nano-rings (nano-rings) at unequal distances on the surface in the one-dimensional length direction. The present invention uses chemical vapor deposition to discontinuously cover the silicon carbide nanofibers. Chemically homogeneous ring-shaped silicon carbide; this unique structure of silicon carbide nanofibers can control the growth of silicon carbide by controlling the independent distribution of the two component silicon sources in the chemical vapor deposition reaction and the introduction of metal oxide nanoparticles The local concentration of carbon monoxide and silicon monoxide gas in the phase changes dynamically, and the ring-shaped silicon carbide nanofiber of the present invention and the airgel material prepared by it have not yet been reported; and it is precisely because the present invention adopts The unique structural characteristics of the airgel building block nanofibers make the airgel material prepared by the present invention have more excellent functional properties in terms of mechanics, heat insulation, and wave absorption.

According to some preferred embodiments, step (1) includes the following sub-steps:

(a) silicon powder and silica airgel powder doped with metal oxide nanoparticles are separated and placed in an independent chamber at the bottom of the graphite crucible, and covered with a graphite lid; the present invention places the graphite crucible in the corundum crucible The schematic diagram in, for example, as shown in Figure 1; In the present invention, the bottom of described graphite crucible that adopts has two independent chambers for example;

(b) Place the above-mentioned graphite crucible with silicon source and silica airgel powder doped with metal oxide nanoparticles in a corundum crucible, and completely bury the graphite crucible with carbon powder, and cover Corundum lid;

(c) The corundum crucible is completely covered with graphite paper and placed in a high-temperature atmosphere furnace for chemical vapor deposition reaction. After cooling to room temperature, collect ring-shaped silicon carbide nanofiber coarse material from the graphite cover;

(d) calcining the ring-shaped silicon carbide nanofiber coarse material to obtain the ring-shaped silicon carbide nanofiber; °C, 750 °C or 800 °C), the calcination time is 20-40 min (eg 20 min, 25 min, 30 min, 35 min or 40 min).

According to some specific implementation manners, step (1) includes the following sub-steps:

(a) Silica powder and silica airgel powder doped with metal oxide nanoparticles are separated and placed in a separate chamber at the bottom of a graphite crucible with a specific aspect ratio and a small size, and covered with a graphite lid;

(b) Put the graphite crucible containing the silicon source and the silica airgel powder doped with metal oxide nanoparticles into a larger corundum crucible, and completely bury the graphite crucible with carbon powder , and covered with a corundum lid;

(c) Cover the above-mentioned corundum crucible with graphite paper completely and place it in a high-temperature atmosphere furnace, keep the argon gas in the furnace at a certain pressure, raise it to a high temperature with a certain heating program and maintain it for a period of time to generate a high-temperature vapor deposition reaction, and wait for cooling To room temperature, scrape off the ring-shaped silicon carbide nanofiber coarse material from the graphite cover;

(d) Treat the scraped ring-shaped silicon carbide nanofiber coarse material in a muffle furnace at 700°C to burn off impurities such as residual carbon to obtain pure ring-shaped silicon carbide nanofibers; the present invention carries out chemical vapor deposition reaction A schematic diagram of the ring-shaped silicon carbide nanofiber is obtained, for example as shown in FIG. 2 .

According to some preferred embodiments, the silica airgel powder doped with metal oxide nanoparticles is formed by mixing metal oxide nanoparticles and silica airgel powder.

According to some preferred embodiments, the average particle size of the silicon powder is 0.1-50 μm, preferably 2 μm; the metal oxide nanoparticles are iron oxide nanoparticles, ferric oxide nanoparticles, ferrous oxide nanoparticles, One or more of zirconium nanoparticles, titanium oxide nanoparticles, copper oxide nanoparticles, zinc oxide nanoparticles, titanium oxide nanoparticles, tin oxide nanoparticles, lead oxide nanoparticles, etc., preferably iron oxide nanoparticles; The average particle diameter of the metal oxide nanoparticles is 10-300 nm, preferably 60 nm; the average particle diameter of the silica airgel powder is 1-200 μm, preferably 5 μm; the skeleton of the silica airgel powder The average particle size of the particles is 6-60nm, preferably 20nm. The silica airgel powder is a porous skeleton structure formed by stacking silica nanoparticles. In the present invention, the silica airgel The average particle diameter of the powder (powder particle diameter) is 1-200 μm, and the average particle diameter of the skeleton particles (silicon dioxide nanoparticles) contained in the silica airgel powder is 6-60 nm; and/or the The mass ratio of metal oxide nanoparticles to the silica airgel powder is (0.001-0.05): 1 (for example, 0.001:1, 0.005:1, 0.008:1, 0.01:1, 0.012:1, 0.015: 1, 0.018:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1 or 0.05:1) is preferably 0.012:1; in the present invention, metal oxide nanoparticles Can play the effect of dynamic regulation SiO and CO gas concentration, thereby indirectly regulates the cyclic SiC structure that generates; In the present invention, preferably the mass ratio of described metal oxide nanoparticle and silicon dioxide airgel powder is ( 0.001～0.05): 1, if this mass ratio is too high or too low, it will affect the above-mentioned adjustment process, which is not conducive to obtaining the ring-shaped silicon carbide nanofiber airgel material of the present invention to a certain extent , but tends to obtain SiC nanofibers with smooth surface.

According to some preferred embodiments, the mass ratio of the silicon powder to the silica airgel powder doped with metal oxide nanoparticles is 1:(0.3～1.5) (eg 1:0.3, 1:0.4 , 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5) preferably 1:0.8 In the present invention, it is preferred that the mass ratio of the silicon powder and the silica airgel powder doped with metal oxide nanoparticles is 1: (0.3～1.5), this mass ratio is too high or If it is too low, it will affect the adjustment process of the oxide nanoparticles to dynamically adjust the concentration of SiO and CO gas, which is not conducive to obtaining the ring-shaped silicon carbide nanofiber airgel material of the present invention, but tends to obtain Silicon carbide nanofibers with smooth surfaces.

According to some preferred embodiments, the chemical vapor deposition reaction is carried out in an inert atmosphere, preferably, the inert atmosphere is argon, and when the chemical vapor deposition reaction is carried out, the pressure of the argon gas is 0.01-0.07MPa ( For example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06 or 0.07MPa) is preferably 0.03MPa; the temperature of the chemical vapor deposition reaction is 1200-1600°C (such as 1200°C, 1250°C, 1300°C, 1350°C, 1400°C , 1450°C, 1500°C, 1550°C or 1600°C) is preferably 1350°C; the chemical vapor deposition reaction time is 1 to 8h (for example 1, 2, 3, 4, 5, 6, 7 or 8h) is preferably 4h; and/or the rate of heating to the temperature of the chemical vapor deposition reaction is 2-8°C/min (eg 2, 3, 4, 5, 6, 7 or 8°C/min), preferably 4°C/min.

According to some preferred embodiments, the graphite crucible is cylindrical, and the ratio of the height to the diameter of the graphite crucible is 1:(2～7) (such as 1:2, 1:3, 1:4, 1:5 , 1:6 or 1:7) is preferably 1:3; that is, in the present invention, preferably the aspect ratio of the graphite crucible is 1:(2～7), more preferably 1:3, in the present invention Among them, it is preferred that the aspect ratio of the graphite crucible is 1: (2-7), which is more conducive to obtaining the ring-shaped silicon carbide nanofiber airgel material of the present invention. If the aspect ratio of the graphite crucible is If the value is too large, the SiO gas generated in the reaction is difficult to reach the graphite cover for deposition reaction to form a SiC collar, and if the aspect ratio of the graphite crucible is too small, the SiO gas generated in the reaction will quickly reach the graphite cover for deposition reaction. SiC nanowires tend to be formed, and only with a suitable aspect ratio, the SiO gas and CO gas generated in the reaction will undergo a fine gas phase reaction on the graphite cover, which is conducive to the formation of a ring-shaped nanofiber structure.

According to some preferred embodiments, the loop-shaped silicon carbide nanofiber contained in the loop-shaped silicon carbide nanofiber airgel material comprises a nanofiber backbone and a plurality of nano-loops sleeved on the nanofiber backbone , for example, as shown in Figure 3; preferably, the average diameter of the nanofiber backbone is 30-240nm, and the average diameter of the periphery of the nano-sleeve ring is 35-280nm; preferably, a plurality of the nano-sleeves The rings are sleeved on the nanofiber backbone at unequal intervals.

According to some specific embodiments, the average diameter of the nanofiber backbone of the ring-shaped silicon carbide nanofiber airgel material is 30-240 nm, and a series of rings (nano-rings) are set on the nanofiber backbone at unequal intervals. , the average diameter of the periphery of the nano-ring is 35-280nm, and has a unique microstructure.

According to some preferred embodiments, the mass fraction of ring-shaped silicon carbide nanofibers contained in the nanofiber dispersion is 0.07% to 7% (such as 0.07%, 1%, 1.5%, 2%, 2.5%, 3% %, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5% or 7%) is preferably 1.5 to 5%, more preferably 2.5%; and/or the time for liquid nitrogen freezing is 5 to 5%. 60 min (eg 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60 min) is preferably 20 min.

According to some preferred embodiments, the freeze-drying is carried out in a freeze-drying machine. During the freeze-drying process, the temperature of the chamber of the freeze-drying machine is controlled to be 10-35° C., and the temperature of the cold trap of the freeze-drying machine is -80°C～-50°C, the pressure of the freeze-drying is 1-30Pa, the time of the freeze-drying is 24-96h; and/or the temperature of the annealing treatment is 800-1100°C (such as 800°C, 850°C °C, 900 °C, 950 °C, 1000 °C, 1050 °C or 1100 °C) is preferably 900 °C, and the time of the annealing treatment is 0.5 to 12 hours (such as 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12h) is preferably 2h.

In a second aspect, the present invention provides the ring-shaped silicon carbide nanofiber airgel material prepared by the preparation method described in the first aspect of the present invention; preferably, the ring-shaped silicon carbide nanofiber airgel The material has one or more of the following properties: the tensile elongation at break of the ring-shaped silicon carbide nanofiber airgel material is 30-40%, and the maximum rebound rate is 100% under the maximum compression deformation of 95%, It exhibits excellent mechanical properties such as flexibility and elasticity; the thermal conductivity of the ring-shaped silicon carbide nanofiber airgel material at room temperature is 0.018-0.021W/m·K, showing super heat insulation capability; the The ring-shaped silicon carbide nanofiber aerogel has excellent microwave absorption performance in the frequency range of 2-18GHz, the matching thickness is 3mm, and the minimum reflection loss (RL) reaches -50~-55dB at 10.5GHz, effectively absorbing microwave Band (RL<-10dB) reaches 6.8-7.5GHz at its widest.

The present invention provides a ring-shaped silicon carbide nanofiber in a third aspect, and the ring-shaped silicon carbide nanofiber is prepared by the following method:

Utilize silicon powder, silicon dioxide airgel powder doped with metal oxide nanoparticles and carbon powder to carry out chemical vapor deposition reaction to obtain ring-shaped silicon carbide nanofibers; The specific parameters of the silicon carbide nanofibers may be the same as the preparation of the ring-shaped silicon carbide nanofibers involved in the first aspect of the present invention.

According to some preferred embodiments, preparing the ring-shaped silicon carbide nanofibers includes the following sub-steps:

(a) silicon powder and silica airgel powder doped with metal oxide nanoparticles are separated and placed in an independent chamber at the bottom of the graphite crucible, and covered with a graphite lid;

(b) Place the above-mentioned graphite crucible with silicon source and silica airgel powder doped with metal oxide nanoparticles in a corundum crucible, and completely bury the graphite crucible with carbon powder, and cover Corundum lid;

(c) The corundum crucible is completely covered with graphite paper and placed in a high-temperature atmosphere furnace for chemical vapor deposition reaction. After cooling to room temperature, collect ring-shaped silicon carbide nanofiber coarse material from the graphite cover;

(d) calcining the ring-shaped silicon carbide nanofiber coarse material to obtain the ring-shaped silicon carbide nanofiber; preferably, the temperature of the calcination is 600-800° C. 40min.

According to some preferred embodiments, the silica airgel powder doped with metal oxide nanoparticles is formed by mixing metal oxide nanoparticles and silica airgel powder; the average particle size of the silica powder The diameter is 0.1-50 μm, preferably 2 μm; the metal oxide nanoparticles are iron oxide nanoparticles, ferric oxide nanoparticles, ferrous oxide nanoparticles, zirconia nanoparticles, titanium oxide nanoparticles, copper oxide nanoparticles, One or more of zinc oxide nanoparticles, titanium oxide nanoparticles, tin oxide nanoparticles, and lead oxide nanoparticles; the average particle diameter of the metal oxide nanoparticles is 10 to 300 nm, preferably 60 nm; the dioxide The average particle diameter of the silica airgel powder is 1-200 μm, preferably 5 μm; the average particle diameter of the skeleton particles of the silica airgel powder is 6-60 nm, preferably 20 nm; and/or the metal oxide nano The mass ratio of particles to the silica airgel powder is (0.001-0.05):1, preferably 0.012:1.

According to some preferred embodiments, the mass ratio of the silicon powder to the silica airgel powder doped with metal oxide nanoparticles is 1: (0.3-1.5), preferably 1:0.8; the chemical The vapor deposition reaction is carried out in an inert atmosphere, preferably, the inert atmosphere is argon, and when the chemical vapor deposition reaction is carried out, the pressure of the argon gas is 0.01-0.07MPa, preferably 0.03MPa; the chemical vapor deposition reaction The temperature is 1200-1600°C, preferably 1350°C; the time of the chemical vapor deposition reaction is 1-8h, preferably 4h; and/or the rate of heating up to the temperature of the chemical vapor deposition reaction is 2-8°C/min, preferably 4°C/min.

According to some preferred embodiments, when the chemical vapor deposition reaction is performed, the silicon powder and the silica airgel powder doped with metal oxide nanoparticles are separated and placed in an independent chamber at the bottom of the graphite crucible, More preferably, the graphite crucible is cylindrical, and the ratio of the height to the diameter of the graphite crucible is 1: (2-7), preferably 1:3.

According to some preferred embodiments, the ring-shaped silicon carbide nanofiber comprises a nanofiber backbone and a plurality of nano-rings sleeved on the nanofiber backbone; preferably, the average diameter of the nanofiber backbone is 30-240nm, the average outer diameter of the nano-ring is 35-280nm; preferably, a plurality of the nano-rings are sleeved on the nanofiber trunk at unequal intervals.

The present invention will be further described below by means of examples, but the protection scope of the present invention is not limited to these examples.

Example 1

1. Mix 0.024g iron oxide nanoparticles (average particle diameter 60nm) with 2g silica airgel powder (average particle diameter 5μm, average particle diameter 20nm of skeleton particle) to obtain the iron oxide nanoparticle doped Silica airgel powder; 2.53g of silicon powder (average particle diameter 2 μm) and 2.024g of silica airgel powder doped with iron oxide nanoparticles are respectively placed in a small-sized cylindrical graphite crucible (height 3cm, diameter 9cm, length-to-diameter ratio is 1:3) in two independent chambers at the bottom, and cover the graphite lid (graphite crucible lid); The above-mentioned silicon dioxide that is equipped with silicon powder and doped with iron oxide nanoparticles is gas-condensed Put the graphite crucible of rubber powder into a larger corundum crucible (height 6cm, diameter 15cm), and pour carbon powder (coke powder) into the corundum crucible until the graphite crucible is completely buried, and cover the corundum lid. Place the above-mentioned corundum crucible in a high-temperature atmosphere furnace, control the atmosphere in the furnace to be 0.03MPa argon, raise the temperature to 1350°C at a rate of 4°C/min, and keep it at this temperature for 4h (1350°C chemical vapor deposition for 4h), Cool naturally to room temperature, scrape the ring-shaped silicon carbide nanofiber coarse material from the graphite crucible lid, and calcinate it in an air atmosphere muffle furnace at 700°C for 30 minutes to completely remove the residual carbon, and obtain the ring-shaped silicon carbide nanofiber ; In this embodiment, 10 groups of batch experiments were carried out in the same method as in step ①, and the ring-shaped silicon carbide nanofibers obtained in 10 groups of experiments were collected together.

②Add 100g of water and 2.5g of the above ring-shaped silicon carbide nanofibers to the beaker, and stir for 2 hours at a stirring speed of 2000rpm to form a uniform and stable dispersed nanofiber dispersion; put the beaker containing the nanofiber dispersion into liquid nitrogen Quickly freeze in medium for 20min to obtain nanofiber gel.

③Put the above-mentioned nanofiber gel into a freeze dryer for freeze drying. The pressure inside the freeze dryer is controlled below 20Pa, the temperature of the freeze dryer chamber is controlled at 25°C, and the temperature of the freeze-drying cold trap is controlled at -70°C. After freeze-drying for 48 hours, the nanofiber airgel was obtained; put the nanofiber airgel into a corundum crucible, put it into an air atmosphere muffle furnace at a temperature of 900°C for annealing treatment for 2 hours, take it out and cool it to room temperature, that is A ring-shaped silicon carbide nanofiber airgel material is obtained.

Example 2

Embodiment 2 is basically the same as Embodiment 1, the difference is:

① Mix 0.002g iron oxide nanoparticles (average particle diameter 60nm) with 2g silica airgel powder (average particle diameter 5μm, average particle diameter 20nm of the skeleton particle) to obtain the iron oxide nanoparticle doped Silica airgel powder; 6.67g of silicon powder (average particle diameter 2 μm) and 2.002g of silica airgel powder doped with iron oxide nanoparticles are respectively placed in a small-sized cylindrical graphite crucible (height 3cm, diameter 9cm, length-to-diameter ratio is 1:3) in two independent chambers at the bottom, and cover the graphite lid (graphite crucible lid); The above-mentioned silicon dioxide that is equipped with silicon powder and doped with iron oxide nanoparticles is gas-condensed Put the graphite crucible of rubber powder into a larger corundum crucible (height 6cm, diameter 15cm), and pour carbon powder (coke powder) into the corundum crucible until the graphite crucible is completely buried, and cover the corundum lid. Place the above-mentioned corundum crucible in a high-temperature atmosphere furnace, control the atmosphere in the furnace to be 0.03MPa argon, raise the temperature to 1350°C at a rate of 4°C/min, and keep it at this temperature for 4h (1350°C chemical vapor deposition for 4h), Cool naturally to room temperature, scrape the ring-shaped silicon carbide nanofiber coarse material from the graphite crucible lid, and calcinate it in an air atmosphere muffle furnace at 700°C for 30 minutes to completely remove the residual carbon, and obtain the ring-shaped silicon carbide nanofiber ; In this embodiment, 10 groups of batch experiments were carried out in the same method as in step ①, and the ring-shaped silicon carbide nanofibers obtained in 10 groups of experiments were collected together.

Example 3

Embodiment 3 is basically the same as Embodiment 1, the difference is:

① Mix 0.1g iron oxide nanoparticles (average particle diameter 60nm) with 2g silica airgel powder (average particle diameter 5μm, average particle diameter 20nm of the skeleton particles) to obtain the iron oxide nanoparticles doped Silica airgel powder; 1.4g silicon powder (average particle diameter 2μm) and 2.1g silica airgel powder doped with iron oxide nanoparticles are respectively placed in a small-sized cylindrical graphite crucible (height 3cm, diameter 9cm, length-to-diameter ratio is 1:3) in two independent chambers at the bottom, and cover the graphite lid (graphite crucible lid); The above-mentioned silicon dioxide that is equipped with silicon powder and doped with iron oxide nanoparticles is gas-condensed Put the graphite crucible of rubber powder into a larger corundum crucible (height 6cm, diameter 15cm), and pour carbon powder (coke powder) into the corundum crucible until the graphite crucible is completely buried, and cover the corundum lid. Place the above-mentioned corundum crucible in a high-temperature atmosphere furnace, control the atmosphere in the furnace to be 0.03MPa argon, raise the temperature to 1350°C at a rate of 4°C/min, and keep it at this temperature for 4h (1350°C chemical vapor deposition for 4h), Cool naturally to room temperature, scrape the ring-shaped silicon carbide nanofiber coarse material from the graphite crucible lid, and calcinate it in an air atmosphere muffle furnace at 700°C for 30 minutes to completely remove the residual carbon, and obtain the ring-shaped silicon carbide nanofiber ; In this embodiment, 10 groups of batch experiments were carried out in the same method as in step ①, and the ring-shaped silicon carbide nanofibers obtained in 10 groups of experiments were collected together.

Example 4

Embodiment 4 is basically the same as Embodiment 1, the difference is:

① Mix 0.0016g iron oxide nanoparticles (average particle diameter 60nm) with 2g silica airgel powder (average particle diameter 5μm, average particle diameter 20nm of the skeleton particle) to obtain the iron oxide nanoparticle doped Silica airgel powder; 10.008g of silicon powder (average particle diameter 2μm) and 2.0016g of silica airgel powder doped with iron oxide nanoparticles are respectively placed in a small-sized cylindrical graphite crucible (height 3cm, diameter 9cm, length-to-diameter ratio is 1:3) in two independent chambers at the bottom, and cover the graphite lid (graphite crucible lid); The above-mentioned silicon dioxide that is equipped with silicon powder and doped with iron oxide nanoparticles is gas-condensed Put the graphite crucible of rubber powder into a larger corundum crucible (height 6cm, diameter 15cm), and pour carbon powder (coke powder) into the corundum crucible until the graphite crucible is completely buried, and cover the corundum lid. Place the above-mentioned corundum crucible in a high-temperature atmosphere furnace, control the atmosphere in the furnace to be 0.03MPa argon, raise the temperature to 1350°C at a rate of 4°C/min, and keep it at this temperature for 4h (1350°C chemical vapor deposition for 4h), Cool naturally to room temperature, scrape the ring-shaped silicon carbide nanofiber coarse material from the graphite crucible lid, and calcinate it in an air atmosphere muffle furnace at 700°C for 30 minutes to completely remove the residual carbon, and obtain the ring-shaped silicon carbide nanofiber ; In this embodiment, 10 groups of batch experiments were carried out in the same method as in step ①, and the ring-shaped silicon carbide nanofibers obtained in 10 groups of experiments were collected together.

Example 5

Embodiment 5 is basically the same as Embodiment 1, the difference is:

1. Mix 0.12g iron oxide nanoparticles (average particle diameter 60nm) with 2g silica airgel powder (average particle diameter 5μm, average particle diameter 20nm of skeleton particle) to obtain the iron oxide nanoparticle doped Silica airgel powder; 1.325g silicon powder (average particle diameter 2μm) and 2.12g silica airgel powder doped with iron oxide nanoparticles are respectively placed in a small-sized cylindrical graphite crucible (height 3cm, diameter 9cm, length-to-diameter ratio is 1:3) in two independent chambers at the bottom, and cover the graphite lid (graphite crucible lid); The above-mentioned silicon dioxide that is equipped with silicon powder and doped with iron oxide nanoparticles is gas-condensed Put the graphite crucible of rubber powder into a larger corundum crucible (height 6cm, diameter 15cm), and pour carbon powder (coke powder) into the corundum crucible until the graphite crucible is completely buried, and cover the corundum lid. Place the above-mentioned corundum crucible in a high-temperature atmosphere furnace, control the atmosphere in the furnace to be 0.03MPa argon, raise the temperature to 1350°C at a rate of 4°C/min, and keep it at this temperature for 4h (1350°C chemical vapor deposition for 4h), Cool naturally to room temperature, scrape the ring-shaped silicon carbide nanofiber coarse material from the graphite crucible lid, and calcinate it in an air atmosphere muffle furnace at 700°C for 30 minutes to completely remove the residual carbon, and obtain the ring-shaped silicon carbide nanofiber ; In this embodiment, 10 groups of batch experiments were carried out in the same method as in step ①, and the ring-shaped silicon carbide nanofibers obtained in 10 groups of experiments were collected together.

Example 6

Embodiment 6 is basically the same as Embodiment 1, the difference is:

In step ①, the small-sized cylindrical graphite crucible used has a height of 4.5 cm, a diameter of 9 cm, and an aspect ratio of 1:2.

Example 7

Embodiment 7 is basically the same as Embodiment 1, the difference is:

In step ①, the small-sized cylindrical graphite crucible used has a height of 1.3 cm, a diameter of 9 cm, and an aspect ratio of 1:7.

Example 8

Embodiment 8 is basically the same as Embodiment 1, the difference is:

In step ①, the height of the small-sized cylindrical graphite crucible is 9 cm, the diameter is 9 cm, and the aspect ratio is 1:1, and the height of the used corundum crucible is 12 cm, and the diameter is 15 cm.

Example 9

Embodiment 9 is basically the same as Embodiment 1, the difference is:

In step ①, the small-sized cylindrical graphite crucible used has a height of 1.1 cm, a diameter of 9 cm, and an aspect ratio of 1:8.

Comparative example 1

1. Mix 0.024g iron oxide nanoparticles (average particle diameter 60nm) with 2g silica airgel powder (average particle diameter 5μm, average particle diameter 20nm of skeleton particle) to obtain the iron oxide nanoparticle doped Silica airgel powder; 2.53g silicon powder (average particle diameter 2 μ m) and 2.024g doped with the silica airgel powder of iron oxide nanoparticles are mixed uniformly to obtain a silicon source; the silicon source is placed in In the bottom chamber (the graphite crucible bottom that adopts has only one chamber) of small size cylindrical graphite crucible (height 3cm, diameter 9cm, aspect ratio is 1:3), and cover graphite lid (graphite crucible lid); The above-mentioned graphite crucible equipped with a silicon source is placed in a larger corundum crucible (height 6cm, diameter 15cm), and carbon powder (coke powder) is poured into the corundum crucible until the graphite crucible is completely buried, and the corundum lid is covered. Place the above-mentioned corundum crucible in a high-temperature atmosphere furnace, control the atmosphere in the furnace to be 0.03MPa argon, raise the temperature to 1350°C at a rate of 4°C/min, and keep it at this temperature for 4h (1350°C chemical vapor deposition for 4h), Naturally cool to room temperature, scrape off the silicon carbide nanofiber coarse material from the graphite crucible lid, and calcinate in an air atmosphere muffle furnace at 700°C for 30 minutes to completely remove residual carbon to obtain silicon carbide nanofibers, which cannot be obtained in this comparative example. Annular silicon carbide nanofibers; in this comparative example, 10 groups of batch experiments were carried out in the same method as in step ①, and the silicon carbide nanofibers obtained in the 10 groups of experiments were collected together.

②Add 100g of water and 2.5g of the above-mentioned silicon carbide nanofibers to the beaker, and stir at a stirring speed of 2000rpm for 2h to form a uniform and stable dispersed nanofiber dispersion; put the beaker containing the nanofiber dispersion into liquid nitrogen and freeze quickly After 20 minutes, the nanofiber gel was obtained.

③Put the above-mentioned nanofiber gel into a freeze dryer for freeze drying. The pressure inside the freeze dryer is controlled below 20Pa, the temperature of the freeze dryer chamber is controlled at 25°C, and the temperature of the freeze-drying cold trap is controlled at -70°C. After freeze-drying for 48 hours, the nanofiber airgel was obtained; put the nanofiber airgel into a corundum crucible, put it into an air atmosphere muffle furnace at a temperature of 900°C for annealing treatment for 2 hours, take it out and cool it to room temperature, that is A silicon carbide nanofiber airgel material is obtained.

Comparative example 2

① Mix 0.024g iron oxide nanoparticles (average particle size 60nm) with 2.53g silicon powder (average particle size 2μm) to obtain silicon powder doped with iron oxide nanoparticles, and then place it on a small-sized cylindrical graphite Crucible (height 3cm, diameter 9cm, aspect ratio is 1:3) in the bottom chamber (the graphite crucible bottom that adopts has only one chamber), and cover graphite lid (graphite crucible lid); Place the graphite crucible of silicon powder with iron oxide nanoparticles into a larger corundum crucible (height 6cm, diameter 15cm), and pour carbon powder (coke powder) into the corundum crucible until the graphite crucible is completely buried, and cover Corundum cover. Place the above-mentioned corundum crucible in a high-temperature atmosphere furnace, control the atmosphere in the furnace to be 0.03MPa argon, raise the temperature to 1350°C at a rate of 4°C/min, and keep it at this temperature for 4h (1350°C chemical vapor deposition for 4h), Naturally cool to room temperature, scrape off the coarse material of silicon carbide nanofibers from the lid of the graphite crucible, and calcinate in an air atmosphere muffle furnace at 700°C for 30 minutes to completely remove the residual carbon to obtain silicon carbide nanofibers, which cannot be obtained in this comparative example Ring-shaped silicon carbide nanofibers; in this comparative example, 10 groups of batch experiments were carried out in the same way as in step ①, and the silicon carbide nanofibers obtained in the 10 groups of experiments were collected together.

②Add 100g of water and 2.5g of the above-mentioned silicon carbide nanofibers to the beaker, and stir at a stirring speed of 2000rpm for 2h to form a uniform and stable dispersed nanofiber dispersion; put the beaker containing the nanofiber dispersion into liquid nitrogen and freeze quickly After 20 minutes, the nanofiber gel was obtained.

③Put the above-mentioned nanofiber gel into a freeze dryer for freeze drying. The pressure inside the freeze dryer is controlled below 20Pa, the temperature of the freeze dryer chamber is controlled at 25°C, and the temperature of the freeze-drying cold trap is controlled at -70°C. After freeze-drying for 48 hours, the nanofiber airgel was obtained; put the nanofiber airgel into a corundum crucible, put it into an air atmosphere muffle furnace at a temperature of 900°C for annealing treatment for 2 hours, take it out and cool it to room temperature, that is A silicon carbide nanofiber airgel material is obtained.

Comparative example 3

① Place 2.53g of silicon powder (average particle size 2μm) and 2.024g of silica airgel powder on the bottom two of a small cylindrical graphite crucible (height 3cm, diameter 9cm, aspect ratio 1:3). In the independent chamber, and cover graphite lid (graphite crucible lid); The above-mentioned graphite crucible that silicon powder and silica airgel powder are housed is placed in the larger corundum crucible (height 6cm, diameter 15cm), And pour carbon powder (coke powder) into the corundum crucible until the graphite crucible is completely buried, and cover the corundum lid. Place the above-mentioned corundum crucible in a high-temperature atmosphere furnace, control the atmosphere in the furnace to be 0.03MPa argon, raise the temperature to 1350°C at a rate of 4°C/min, and keep it at this temperature for 4h (1350°C chemical vapor deposition for 4h), Naturally cool to room temperature, scrape off the coarse material of silicon carbide nanofibers from the lid of the graphite crucible, and calcinate in an air atmosphere muffle furnace at 700°C for 30 minutes to completely remove the residual carbon to obtain silicon carbide nanofibers, which cannot be obtained in this comparative example Ring-shaped silicon carbide nanofibers; in this comparative example, 10 groups of batch experiments were carried out in the same way as in step ①, and the silicon carbide nanofibers obtained in the 10 groups of experiments were collected together.

②Add 100g of water and 2.5g of the above-mentioned silicon carbide nanofibers to the beaker, and stir at a stirring speed of 2000rpm for 2h to form a uniform and stable dispersed nanofiber dispersion; put the beaker containing the nanofiber dispersion into liquid nitrogen and freeze quickly After 20 minutes, the nanofiber gel was obtained.

③Put the above-mentioned nanofiber gel into a freeze dryer for freeze drying. The pressure inside the freeze dryer is controlled below 20Pa, the temperature of the freeze dryer chamber is controlled at 25°C, and the temperature of the freeze-drying cold trap is controlled at -70°C. After freeze-drying for 48 hours, the nanofiber airgel was obtained; put the nanofiber airgel into a corundum crucible, put it into an air atmosphere muffle furnace at a temperature of 900°C for annealing treatment for 2 hours, take it out and cool it to room temperature, that is A silicon carbide nanofiber airgel material is obtained.

Comparative example 4

①Put 100g of calcium carbonate and 30g of activated carbon into a stainless steel ball mill jar, and place 300g of zirconia grinding balls, and ball mill at a speed of 100r/min for 5h to obtain a carbon source with a particle size of 340nm.

②Put 28g of silicon powder and 60g of silicon dioxide into a stainless steel ball mill jar, and place 200g of zirconia grinding balls, and ball mill at a rate of 200r/min for 4 hours to obtain a silicon source with a particle size of 200nm.

③Put 50g of carbon source and 100g of silicon source in a graphite crucible, mix them evenly, and carry out a chemical vapor deposition reaction at 1500°C for 5 hours under an argon atmosphere, collect the product on the surface of the graphite crucible cover, and obtain a silicon carbide fiber airgel material .

Comparative example 5

① Cut the carbon fiber cloth into a size of 30mm×60mm, soak it in absolute ethanol for 1 hour, then soak it in 10% sodium hydroxide solution for 1 hour, rinse it, and dry it to get the pretreated carbon fiber cloth.

②Impregnation treatment: soak the pretreated carbon fiber cloth in 0.1mol/L Ni(NO ₃ ) ₂ solution for 1 hour, and dry it at 70°C for 2 hours to obtain the carbon fiber cloth raw material loaded with catalyst.

③ Sintering: Lay the catalyst-loaded carbon fiber cloth raw material on the bottom of the corundum crucible, and place the reaction silicon source on the catalyst-loaded carbon fiber cloth raw material to obtain a corundum crucible filled with reactants; use inert gas (argon) as protection gas, sinter the corundum crucible containing the reactants at a temperature of 1500°C for 3 hours, and cool to room temperature to obtain test tube brush-shaped SiC nanowires; The molar ratio of C element in cloth is 1:2.

The present invention has tested the performance index of the material that embodiment 1～9 and comparative example 1～5 finally make, and test result is as shown in table 1; In the present invention, 95% compressive set is material in thickness direction The amount of compression accounts for 95% of the initial thickness of the material; in Table 1, the microwave absorption performance of the material is tested in the matching thickness of 3mm, and the frequency range is 2-18GHz. The minimum reflection loss (RL) is the minimum reflection loss corresponding to 10.5GHz. The effective absorption bandwidth is the effective absorption bandwidth of reflection loss <-10dB; the tensile elongation at break in Table 1 refers to the GB/T6344-2008 standard to measure the tensile stress-strain characteristics to obtain the tensile elongation at break.

Table 1: Performance indicators of the materials prepared in Examples 1-9 and Comparative Examples 1-5.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (27)

1. A method for preparing a collar-like silicon carbide nanofiber aerogel material, the method comprising the steps of:

(1) Performing chemical vapor deposition reaction by using silicon powder, silicon dioxide aerogel powder doped with metal oxide nano particles and carbon powder to obtain collar-shaped silicon carbide nano fibers; when chemical vapor deposition reaction is carried out, silicon powder and silicon dioxide aerogel powder doped with metal oxide nano particles are separately placed in an independent cavity at the bottom of a graphite crucible, and a graphite cover is covered; placing the graphite crucible in a corundum crucible, completely burying the graphite crucible by using carbon powder, and covering a corundum cover; the graphite crucible is cylindrical, and the ratio of the height to the diameter of the graphite crucible is 1: (2-7); the silicon dioxide aerogel powder doped with the metal oxide nano particles is formed by mixing the metal oxide nano particles with silicon dioxide aerogel powder; the metal oxide nanoparticles are one or more of ferric oxide nanoparticles, ferroferric oxide nanoparticles, ferrous oxide nanoparticles, zirconium oxide nanoparticles, copper oxide nanoparticles, zinc oxide nanoparticles, titanium oxide nanoparticles, tin oxide nanoparticles and lead oxide nanoparticles; the mass ratio of the metal oxide nano particles to the silicon dioxide aerogel powder is (0.001-0.05): 1, a step of; the mass ratio of the silicon powder to the silicon dioxide aerogel powder doped with the metal oxide nano particles is 1: (0.3 to 1.5);

(2) Uniformly dispersing the collar-shaped silicon carbide nano fibers with water to obtain nano fiber dispersion liquid, and then performing liquid nitrogen freezing on the nano fiber dispersion liquid to obtain nano fiber gel;

(3) And sequentially carrying out freeze drying and annealing treatment on the nanofiber gel to obtain the collar-shaped silicon carbide nanofiber aerogel material.

2. The method of claim 1, wherein step (1) comprises the sub-steps of:

(a) Silicon powder and silicon dioxide aerogel powder doped with metal oxide nano particles are separately placed in an independent cavity at the bottom of a graphite crucible, and a graphite cover is covered;

(b) Placing the graphite crucible in a corundum crucible, completely burying the graphite crucible by using carbon powder, and covering a corundum cover;

(c) Completely coating the corundum crucible with graphite paper, placing the corundum crucible into a high-temperature atmosphere furnace for chemical vapor deposition reaction, cooling to room temperature, and collecting collar-shaped silicon carbide nanofiber coarse materials from a graphite cover;

(d) Calcining the coarse material of the collar-shaped silicon carbide nanofiber to obtain the collar-shaped silicon carbide nanofiber.

3. The preparation method according to claim 2, characterized in that:

The calcination temperature is 600-800 ℃, and the calcination time is 20-40 min.

4. The method of manufacturing according to claim 1, characterized in that:

the average grain diameter of the silicon powder is 0.1-50 mu m;

the average particle size of the metal oxide nano particles is 10-300 nm;

the average particle size of the silica aerogel powder is 1-200 mu m;

the average particle size of skeleton particles of the silica aerogel powder is 6-60 nm; and/or

The mass ratio of the metal oxide nano particles to the silicon dioxide aerogel powder is 0.012:1.

5. The method of manufacturing according to claim 4, wherein:

the average grain diameter of the silicon powder is 2 mu m.

6. The method of manufacturing according to claim 4, wherein:

the average particle diameter of the metal oxide nanoparticles is 60nm.

7. The method of manufacturing according to claim 4, wherein:

the average particle diameter of the silica aerogel powder is 5 μm.

8. The method of manufacturing according to claim 4, wherein:

the average particle diameter of the framework particles of the silica aerogel powder is 20nm.

9. The method of manufacturing according to claim 1, characterized in that:

the mass ratio of the silicon powder to the silicon dioxide aerogel powder doped with the metal oxide nano particles is 1:0.8;

The chemical vapor deposition reaction is carried out in an inert atmosphere;

the temperature of the chemical vapor deposition reaction is 1200-1600 ℃;

the time of the chemical vapor deposition reaction is 1-8 hours; and/or

The temperature is raised to the temperature of the chemical vapor deposition reaction at a rate of 2-8 ℃/min.

10. The method of manufacturing according to claim 9, wherein:

the inert atmosphere is argon, and the argon pressure is 0.01-0.07 MPa when the chemical vapor deposition reaction is carried out.

11. The method of manufacturing according to claim 10, wherein:

the argon pressure was 0.03MPa when the chemical vapor deposition reaction was performed.

12. The method of manufacturing according to claim 9, wherein:

the temperature of the chemical vapor deposition reaction is 1350 ℃.

13. The method of manufacturing according to claim 9, wherein:

the time of the chemical vapor deposition reaction is 4 hours.

14. The method of manufacturing according to claim 9, wherein:

the rate of temperature rise to the temperature of the chemical vapor deposition reaction was 4 ℃/min.

15. The method of manufacturing according to claim 1, characterized in that:

the ratio of the height to the diameter of the graphite crucible is 1:3.

16. The production method according to any one of claims 1 to 15, characterized in that:

the collar-shaped silicon carbide nanofiber contained in the collar-shaped silicon carbide nanofiber aerogel material comprises a nanofiber backbone and a plurality of nanometer collars sleeved on the nanofiber backbone.

17. The method of manufacturing according to claim 16, wherein:

the average diameter of the nanofiber trunk is 30-240 nm, and the average diameter of the periphery of the nanometer lantern ring is 35-280 nm.

18. The method of manufacturing according to claim 16, wherein:

the plurality of nanometer lantern rings are sleeved on the nanofiber trunk at unequal intervals.

19. The production method according to any one of claims 1 to 15, characterized in that:

the mass fraction of the collar-shaped silicon carbide nanofibers contained in the nanofiber dispersion liquid is 0.07% -7%; and/or

The time for freezing liquid nitrogen is 5-60 min.

20. The method of manufacturing according to claim 19, wherein:

the mass fraction of the collar-shaped silicon carbide nanofibers contained in the nanofiber dispersion was 2.5%.

21. The method of manufacturing according to claim 19, wherein:

The time for liquid nitrogen freezing was 20min.

22. The production method according to any one of claims 1 to 15, characterized in that:

the freeze drying is carried out in a freeze dryer, in the freeze drying process, the temperature of a chamber of the freeze dryer is controlled to be 10-35 ℃, the temperature of a cold trap of the freeze dryer is controlled to be-80 ℃ to-50 ℃, the pressure of the freeze drying is 1-30 Pa, and the time of the freeze drying is 24-96 h; and/or

The temperature of the annealing treatment is 800-1100 ℃, and the time of the annealing treatment is 0.5-12 h.

23. The method of manufacturing according to claim 22, wherein:

the temperature of the annealing treatment is 900 ℃.

24. The method of manufacturing according to claim 22, wherein:

the annealing treatment time is 2h.

25. A collar-like silicon carbide nanofiber aerogel material made by the method of any of claims 1 to 24.

26. The collar-like silicon carbide nanofiber aerogel material as claimed in claim 25, wherein the collar-like silicon carbide nanofiber aerogel material has one or more of the following properties:

the elongation at break of the collar-shaped silicon carbide nanofiber aerogel material is 30-40%, and the rebound rate is 100% at the maximum compression deformation of 95%;

The ambient temperature thermal conductivity of the collar-shaped silicon carbide nanofiber aerogel material is 0.018-0.021W/(m.K);

the collar-shaped silicon carbide nanofiber aerogel material has excellent microwave absorption performance in the frequency range of 2-18GHz, the matching thickness is 3mm, the minimum reflection loss is-50 to-55 dB at 10.5GHz, and the effective absorption bandwidth of the reflection loss of-10 dB is 6.8-7.5 GHz.

27. The collar-shaped silicon carbide nanofiber is characterized by being prepared by the following steps:

performing chemical vapor deposition reaction by using silicon powder, silicon dioxide aerogel powder doped with metal oxide nano particles and carbon powder to obtain collar-shaped silicon carbide nano fibers;

the silica aerogel powder doped with the metal oxide nanoparticles is formed by mixing metal oxide nanoparticles and silica aerogel powder, the metal oxide nanoparticles are one or more of ferric oxide nanoparticles, ferroferric oxide nanoparticles, ferrous oxide nanoparticles, zirconium oxide nanoparticles, copper oxide nanoparticles, zinc oxide nanoparticles, titanium oxide nanoparticles, tin oxide nanoparticles and lead oxide nanoparticles, and the mass ratio of the metal oxide nanoparticles to the silica aerogel powder is (0.001-0.05): 1, a step of; the mass ratio of the silicon powder to the silicon dioxide aerogel powder doped with the metal oxide nano particles is 1: (0.3 to 1.5);

When chemical vapor deposition reaction is carried out, silicon powder and silicon dioxide aerogel powder doped with metal oxide nano particles are separately placed in an independent cavity at the bottom of a graphite crucible, and a graphite cover is covered; placing the graphite crucible in a corundum crucible, completely burying the graphite crucible by using carbon powder, and covering a corundum cover; the graphite crucible is cylindrical, and the ratio of the height to the diameter of the graphite crucible is 1: (2-7).

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